Democratic incumbent Nathaniel P. Tallmadge's term had expired and no successor was elected due to the legislature's failure to elect.Incumbent re-electedJanuary 27, 1840 to his former position in a different party.Whig gain.

Incumbent resigned January 13, 1840 after refusing to vote for the Subtreasury Bill as demanded by the Tennessee legislature[1]New senator electedFebruary 26, 1840.Democratic gain.Successor would not be elected to the next term, see below.

Incumbent resigned November 16, 1840 because he could not obey instructions of the North Carolina General Assembly.New senator electedNovember 25, 1840.Whig gain.Successor would also be elected to the next term, see below.

Democratic incumbent William C. Rives's term had expired and no successor was elected due to the legislature's failure to elect.Incumbent re-electedJanuary 18, 1841 to his former position in a different party.Whig gain.

Nathaniel P. Tallmadge had been elected as a Jacksonian Democrat in 1833 to this seat, and his term expired March 3, 1839. An election was held February 5, 1839. Although Tallmadge received the most votes, no candidate received a majority and the seat was declared vacant due to the legislature's failure to elect.

Tallmadge re-took his seat on January 27, 1840,[4] and remained in office until June 17, 1844, when he resigned to be appointed Governor of Wisconsin Territory. Daniel S. Dickinson was appointed to fill the vacancy temporarily, and subsequently elected by the State Legislature to succeed Tallmadge.

DemocratSamuel McKean was elected by the Pennsylvania General Assembly, consisting of the House of Representatives and the Senate, in the 1832–1833 Senate election. Sen. McKean's term was to expire on March 4, 1839, and an election would have occurred during the winter of 1838–1839 elect a Senator for the successive term. The election did not occur, however, due to significant political unrest in Harrisburg, the state capital, over disputed election returns during the Buckshot War. McKean's seat was vacated when his term expired in March 1839 and remained vacant until the General Assembly elected a new Senator in 1840.[5]

The Pennsylvania General Assembly convened on January 14, 1840, to elect a Senator to serve out the remainder of the term that began on March 4, 1839. The results of the vote of both houses combined are as follows: